dwtlsmith

Have 87 F150 with V6.
I starts fine and idles fine until you press the throttle about a quater
Of the way. After that it idles high until you shut it off then back on.
Checked the throttle position sensor and it measures good.

Have checked a couple of other sensors but all seem to be fine. I was wondering if this made any sense or if anyone has any suggestions. Hate to just change parts.

Thanks

Tote-M-Pole

Unless the previous owner put a V6 in this truck it should be the I6 300 ci. Anyway, have you checked for codes? Do this first before throwing $$ at it. Probably something to do with the IAC.

Let us know what you find.

dwtlsmith

Sorry it the factory I6.
I was going to check the codes using the check engine light but it don't exist. Went to replace the bulb but the socket isn't even there. I don't have a code reader and not sure if a digital meter will work but I will see.

Did clean the IAC (was pretty black) and inlet of the throttle body. Seemed better at first. But it idling high again. Did disconnect the coolant temp sensor and it idles fine. The sensor measures good. I cleaned the connections but will idle high when you plug it back in while running.

yardratt2007

I have a similar problem with my 93 6cyl. It revs up when started then idles down until I step on throttle. Then it stays high until I shut it off. The previous owner had a new radiator put in and I noticed what looks like an old temp sensor laying on the block still attached to the harness but not plugged in anywhere. I can't find anyplace for it to go. Thought I'd comment because your issue sounds similar and maybe a coolant sensor is involved. I replaced the IAC and a couple of vacuum lines. No change.

dwtlsmith

Sorry for the delay. Had 4 Wheeler accident.

Turned out to be the throttle position sensor. Seemed good with digital meter but showed bad when scoped.

Thanks